During work with catheters in the operating room, and in the case of certain other interventions, arteries and veins must be pierced with relatively thick, hollow needles to insert catheters. Arteries and veins are often punctured, which are not highly visible and scarcely palpable through the skin. This creates the problem of locating suitable blood vessels in the body with sufficient accuracy to permit them to be punctured thereafter. The known ultrasonic Doppler technique permits a simple and precise location of the sought blood vessels. It is even thereby possible to determine the direction of flow in the individual blood vessel and thus to distinguish and identify arteries and veins.
Disclosed in patent CH 536,635 (Siemens) is a device in which an ultrasonic Doppler probe is permanently mounted at the upper end of the injection cannula. The probe cannot be withdrawn from the cannula after the puncture is made. The cannula is thus provided with a branch to the side for connection of a syringe or tube. With this arrangement it is possible to insert injection cannulae in blood vessels with great accuracy. This technique has not become widely used in practice.